A musical instrument produces an harmonic tone by establishing a standing wave in a resonator, defined herein as a chamber or medium within which a standing wave can be established. The standing wave vibrates at a frequency determined by three separate factors: the medium through which the wave propagates; the length of the resonator; and the conditions at the boundaries (ends) of the resonator. The vibrations in the resonator give rise to a soundwave of comparable frequency that travels through the air to a listener where it is detected as a tone. All tones, both harmonic and pure, are defined by a fundamental frequency v0. Musical notes are harmonic tones and as such consist of components at frequencies that differ from the fundamental frequency; commonly known as overtones or harmonics. The frequency for each harmonic bears a mathematical relationship to the fundamental frequency that characterizes a given tone. Specifically, each harmonic exists at a frequency that is some positive whole number multiple of the fundamental frequency. The harmonic series, the sequence of all harmonics including the fundamental frequency, indicates the mathematical relationship between the harmonics and will depend upon the character of the resonator. In particular, it is the type of resonator and the boundary conditions of said resonator that dictate the harmonic series. For example, the harmonic series for a vibrating string fixed at both ends is 2v0, 3v0, 4v0, etc. where v0 is the fundamental frequency.
Different musical instruments produce tones that share a common fundamental frequency yet are notably different in their tonal character. This difference in tonal character is described as timbre (′tam-bar) and is ascribed to the different harmonic profiles that accompany the fundamental frequency for a given tone. The harmonic profile may be defined herein as a collection of data for audible harmonics including, for example, pitch, volume, inharmonicity and sustain time; the contribution of each having potential effects upon tonal quality. The tone associated with a given musical instrument has a characteristic harmonic profile. It is the difference in the relative contributions among the harmonics for a given note that differentiates one instrument from another. Thus, an A note having a fundamental frequency of 440.00 Hz sounds markedly different if played on a piano or a trumpet.
The timbre of a harmonic tone (though not the pitch) is dependent upon the strength, pitch and length of each harmonic and changes in these factors give rise to subtle changes in the timbre of an harmonic tone. The practice of altering the individual harmonics of a tone to effect a desired tonal quality is referred to as voicing. It is important to appreciate the distinction between tuning and voicing. Tuning of a musical instrument is the correction of pitch in generated tones such that the fundamental frequencies for generated tones is coincident with frequencies that have been established for each tone, the tones corresponding to notes of a musical scale. For example, A4, the fourth A note on the piano scale, is defined by convention as having a fundamental frequency of exactly 440.00 Hz. By contrast, voicing is not measured against any such objective standard but involves adjustment of a tone to conform to some preferred voiced. As such, it can vary between musicians and others who appreciate and can discern subtle changes in tonal quality. Descriptions of tonal quality include bright or hard for excessively loud or tinny sounds, and dull or soft for excessively muted or mushy sounds. Tonal quality is readily and permanently adjusted in many instruments by the physical construction of the instrument, qualities of some portion of the resonator, qualities of the performer or some combination thereof.
Inharmonicity is one aspect of tonal quality of relevance to tones generated from pianos. In the piano, the resonator is called a piano string. However, this is somewhat of a misnomer as the piano generates its distinctive sound because the resonator usually comprises a metal wire bound between two fixed ends at high tension. The wire has an associated stiffniess that results in a departure from an ideal harmonic resonator. The resultant wave comprises a degree of inharmonicity, defined here as the extent to which a given harmonic deviates from its predicted frequency. Harmonic frequencies as calculated from an harmonic series are at frequencies that are whole number multiples of the fundamental frequency. One distinctive quality of the piano's sound originates with the inharmonicity present in some harmonics of the tone from the piano.
Tonal quality in the piano is dependent upon the nature of the collision that generates the standing wave in the resonator (piano string). In particular, piano technicians seek to alter the hammer-string interaction in some way to effect desired changes in the tonal quality of the piano. As each of the 88 keys of the piano keyboard is mechanically linked to one hammer, that strikes one, two or three strings of the piano, the adjustment of the hammer, its properties at the striking surface and the manner in which it strikes at least one piano string will directly impact the harmonic profile, and therefore the tonal quality, of each note. Two functions performed by piano technicians seek to attain desirable harmonic profiles by adjustment of some aspect of the piano hammer: regulation and voicing. Regulation concerns the adjustment of the mechanical action of the hammer, levers and counterweights responsible for propelling the hammer into at least one string, the latter concerns the adjustment of the felt that covers the wooden piano hammer.
Manipulating the felt covering of a piano hammer to effect a change in tonal quality is the manner in which the process of voicing takes place in the piano. Voicing of the piano is typically carried out by an experienced piano technician who has developed three key abilities: 1) detection and identification of subtle changes in tonal quality; and 2) familiarity with and ability to execute the requisite voicing procedures upon the hammer felt; and 3) the experience to gauge the predicted effect of a given voicing procedure upon tonal quality. Voicing procedures may be generalized as those that change the hardness of the felt covering in at least one area of the piano hammer. Felt is a fabric that is formed of hair and/or wool fibers that have been interlaced to form a soft, dense fabric. Voicing procedures alter the hardness of the felt by changing the extent to which the fibers of the felt are interweaved; voicing procedures that soften the felt decrease the degree of interweaving while those procedures that harden the felt increase the degree of interweaving. It should be noted that the position on the hammer felt at which voicing procedures can be carried out is not limited to the striking surface of the hammer. For example, hammers that are judged to be too hard are subjected to a process known as needling in which a specialized needling tool often comprising three needles oriented axially within a holder cuts small threads of the tightly wrapped felt. Needling can take place at the striking surface or the shoulders of the hammer felt. For example, a tone that is judged to be hard at predominantly loud volumes (forte) is indicative of a hammer requiring deep-needling at the shoulders. By contrast, a tone that is judged to be hard at soft (pianissimo) volumes is indicative of a hammer requiring shallow needling at the striking surface. Piano hammer felt can also be filed to shape, smooth, and/or remove soft layers of felt to expose harder layers underneath.
The process of voicing a piano tends to be time- and labor-intensive, placing high burdens upon the operator performing the voicing procedure. Typically, a piano technician performing the voicing plays all the notes on the piano several times at varying volume levels to judge the overall tone of the instrument. Individual notes that are judged as being too bright (hard) or dull (soft) are marked as such and the action of the piano is disengaged. The corresponding hammers are voiced, the action of the piano is re-engaged and each note is re-played to judge the effectiveness of the voicing procedures. The process is repeated until an optimal tonal quality is achieved. It is important to note that the piano cannot be played once the action is disengaged. This can require that the technician repeat the cycle of playing the notes, disengaging the action, and voicing the hammers several times before optimal tonal quality can be achieved.
The success of any given voicing procedure is largely dependent upon the ability of the operator to audibly detect any defects in tonal quality present in a given tone, placing a high premium on the hearing ability of the operator. In particular, an operator must have good hearing in the high frequency range to detect the higher harmonics present in a given tone. Because piano technicians typically encounter volume levels approaching the safe-hearing threshold of 120 dB during the course of their work; high-frequency hearing loss is a problem within the art.
There remains a need within the art for piano voicing procedures that are less subjective and more quantitative. Although there exists software in the art that is capable of describing the tonal quality, we are unaware of any method that can properly and quantitatively correlate a desired tonal quality with a given voicing technique. For example, the Pianalyzer of the Reyburn CyberTuner is a software application that displays pitch, inharmonicity, sustain time in seconds and volume for partials 1–16. However, the Pianalyzer does not suggest an optimal voicing technique to achieve a preferred standard of tonal quality. Thus, the voicing of pianos largely remains a process susceptible to inconsistency. Different operators may perceive different aspects of tonal quality and select different voicing techniques. Indeed, the same operator can perceive tonal quality differently from day to day. Across the broad range of piano technicians, there are differences in the exact manner in which voicing procedures are carried out.
For the reasons described above, there exists a clear need within the art of piano technology for methods that make the voicing of piano hammer felt easier, faster, more accurate and more precise. In particular, there remains a need within the art for a method of adjusting tonal quality in pianos in a consistent and exact process that is independent of human error. In addition, there remains a need within the art for voicing procedures that can assist piano technicians in the diagnosis of tones without undue demands upon operator hearing, time or work. Further, there remains a need within the art for voicing procedures that alleviate the burdens placed upon piano technicians.